Record-Setting Neutron Star Shows Astronomers What It's Made of

By Andrew Moseman | October 28, 2010 10:23 am

neutronstarWhere once there was a star 20 times the size of our sun, now there is a record breaker. Astronomers report this week in Nature that when the huge star went supernova, it collapsed into a neutron star that is heaviest they’ve ever seen, with twice the mass of our sun compacted into a tiny space. Aside from taking its place in the record books, this massive monster could reveal what truly goes on deep in the heart of a deceased star.

The neutron star is part of a binary star system called J1614-2230, in which it and a white dwarf are locked in a spin cycle. Thanks to the neutron star’s steady emission of radio waves and a handy trick of relativity, scientists can measure the size of the two objects despite the fact that they’re 3,000 light years from here.

The astronomers took detailed measurements of the radio pulses that reached Earth. As these pulses, which originate from the rotation of the neutron star, passed by the companion white dwarf, their timing was delayed due to the highly warped nature of spacetime—an effect known as Shapiro delay. In a highly inclined, nearly edge-on system such as J1614-2230 the effect allows astronomers to make very accurate measurements both of the neutron star and its companion. [Ars Technica]

Neutron stars form under incredible pressure when a star goes nova—pressure that can mash protons and electrons together to form neutrons, the thinking goes. Their extreme character, with a mass often greater than our sun packed into an area no bigger than a city, makes neutron stars the perfect test subjects for some weird physics, study author Paul Demorest says.

“Neutron stars are some of the best astronomical objects to probe fundamental physics itself. They are the most dense form of matter that exists in stable configurations,” Demorest [says]. Only black holes are denser. But since light can’t escape from these gravitational pits, black holes keep their inner workings to themselves. [Discovery News]

Still, what happens inside a neutron star is no settled question. Researchers just don’t know exactly how matter behaves when it’s crushed and pummeled into such out-of-this-world densities, and so some astronomers suggest there’s much more to neutron stars than just neutrons.

Rival models suggest that the objects might be made up of the constituents of neutrons — free quarks — or other types of exotic matter, such as ‘hyperons’. [Nature]

However, Demorest says, the most exotic of those constituents—like hyperons and free quarks—could not form a neutron star this massive, so his study may trim the possibilities of what’s stirring inside these star corpses.

“It’s simply that if those particles were formed, the star would get too dense and collapse into a black hole prior to this point,” [he] said. [BBC News]

Related Content:
80beats: Neutron Stars Prove Einstein Right (Again)
80beats: Lost and Found: Supernova Remnant Recaptured by Hubble
80beats: A Baby Neutron Star, Swaddled in a Carbon Atmosphere
DISCOVER: The Case of the Missing Neutron Stars
DISCOVER: A New Type of Star

Image: Casey Reed/Penn State University

  • nick

    Hate to be pedantic (okay, that’s a lie) but electrons and protons don’t come together to form neutrons, neutrons are the chargeless particles already existing inside normal matter that help add mass to the nucleus of an atom – they were discovered when atoms had more mass than the protons and electrons alone could account for, and the amount of neutrons in an atom determines what isotope of an element you have, whereas the amount of protons determines which element you have. (and for the extra curious, the electrons and how they ‘orbit’ determine how atoms bond, or don’t, with one another)

    The electrons and protons were probably lost in the nova. A neutron star is composed of neutrons that have overcome their normal repulsion and are packed together as densely as we can currently imagine matter being (can’t get any closer due to the Pauli exclusion principle – at least as far as we are currently aware).

    Though, it does sound quite logical that you mash some protons and electrons together to get neutrons (i.e. positive + negative = neutral). But neutrons are made up of three quarks, as are protons (though in different configurations, thus the neutral and positive charges, respectively), and electrons themselves are indivisible (as far as we are currently aware).

  • astrohobo

    Nope, nick, you are totally out to lunch here.

    The core of a massive star is already compressed to maximum atomic density such that degenerate electron pressure (the Pauli exclusion principle) is holding it up . This special form of matter is what the white dwarf companion star is made of. When the core reaches the critical mass of 1.4 times solar, and when the degenerate pressure is no longer aided by heat from internal fusion because you can’t get energy out of iron 56 (which the fusion process has built up the atoms into), then it becomes energetically advantageous for the electrons and protons to combine into neutrons (the technical term is neutron drip).

    Note that in ordinary hydrogen fusion, protons and electrons turn into neutrons all the time… in fact, that’s how you get neutrons in the first place. You don’t create neutron/anti-neutron pairs out of raw energy like you can make protons and anti-protons as well as electrons and positrons. To make a helium nucleus consisting of two protons and two neutrons, you start with 4 hydrogen atoms consisting of 1 proton and one electron each.

  • Richard

    The high pressures of the collapse of the interior of a supernova drive the endothermic process

    e + p -> n + neutrino.

    So yes, “electrons and protons do come together to form neutrons” ( plus a neutrino which escapes the supernova.) Look up “inverse beta decay,” or “electron-capture.”

  • Dwayne Stephenson

    Plus, it’s impossible to imagine how a supernova could explode in such a way that the neutrons would magically separate from the electrons and protons to form their own celestial mass.

  • cag

    People like nick are all too common in the world. I’m convinced 90% of the population does not grasp the basics of the Universe. Sad.


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